1. Field of the Invention
The present invention relates to a charged beam apparatus using charged particles such as electrons and ions and a method of cleaning the apparatus, and particularly relates to a charged beam apparatus having a function of cleaning and a method of cleaning the apparatus.
2. Description of the Related Art
In recent years, as the density in integration of an integrated circuit has been improved, limitations have been pointed out with respect to photo-lithography which has been used as the leading technique for forming a fine pattern, while lithography using an electron beam (e.g., an electron beam exposure apparatus) has rapidly developed as a method for overcoming the limitations. In an electron beam exposure apparatus, contaminants stick to electrodes used for deflection or blanking, due to a reaction between scattering electrons or secondary electrons and residual gases, and the contaminants are charged during exposure so that the contaminants serve as factors which change the trajectory of the electron beam. Therefore, it has been necessary to clean electrodes, apertures, and the likes to remove contaminants. As means for solving these problems, an in-situ cleaning method using plasma is well-known (Jpn. Pat. Appln. KOKAI Publication No. 1-22978). The plasma means a state in which respective particles are dissociated into ions and electrons and the entire gas system is substantially electric neutral.
That is, as shown in FIG. 1, a mixture of an O.sub.2 gas and a CF.sub.4 gas is supplied to a plasma generator apparatus 172 provided outside the column 171 of an electron beam exposure apparatus, and plasma generated by microwave-exciting the gas mixture is drawn into the column 171 and is made to flow into two apertures 175, i.e., upper and lower apertures in the column 171, while being exhausted by a rotary pump 174. As a result of this, contaminants of hydrocarbon base sticking to metallic members, such as apertures 175 and a deflection electrode 179 for controlling movements of electrons and the likes, react with ions having a strong oxidizing power and are evaporated, thus removing them from metallic members such as apertures 175, a deflection electrode 179 and the likes. In this figure, reference 176 denotes a gate valve, reference 178 denotes an electron beam generator portion, and reference 178 denotes an exposure chamber. Further, the deflection electrode 179 is retained at a predetermined position by a measure not shown.
However, the cleaning method using plasma as stated above include the following problems. Specifically, ions in plasma used for removing contaminants have a function of fluorinating and oxidizing metal members such as a deflection electrode, thereby forming an oxide film, a fluoride film, and the likes on surfaces of metal members, in addition to a function of removing contaminants, i.e., substances of hydrocarbon base. Since these oxidizing and fluoridating films are insulating materials, these films are slightly charged by scattering electrons and secondary electrons during exposure. Even such slight charging serves as a factor which makes an electron beam drift, and the drifting makes it difficult to form a highly precise pattern. Further, a rapid increase in temperature due to ion-sputtering makes bad influences such as damages the metal members or the mechanical accuracy thereof.
To solve these problems, a method of providing a grid above a cleaning portion thereby to repulse ions and the likes in plasma which serve as factors causing an oxidized film or a fluoride film (Jpn. Pat. Appln. KOKAI Application No. 3-3225). However, in this method, although remarkable changes of color due to oxidization can be avoided, an oxidized film and a fluoride film are still formed so that sufficient cleaning effects cannot be obtained.
In addition, as another method for solving the problems, there is provided a method of removing an oxidized film and a fluoridated film by heating a cleaning portion after cleaning with use of active species having a lower oxidizing power than plasma ions (Jpn. Pat. Appln. KOKAI Publication 5-144716). Further, in this method, it is possible to avoid damages on materials due to sputtering. The active species mean molecules each being electrically neutral, i.e., excited molecules and radicals. A radical is a molecule having unpaired electrons, e.g., an O atom. However, there is a problem that oxidized materials formed on a part made of iron cannot be removed by heating, depending on members of cleaning portions. Further, there is a problem that the active species have an oxidizing power smaller than ions and are easily lost, so that, in a location far from the source of the active species, cleaning abilities are lost and sufficient cleaning cannot be performed.
In addition, since the internal space of the column 171 is divided into a plurality of independent areas by partitions having a small exhausting conductance such as apertures 175, there is a problem that the cleaning ability is lost when plasma or active species pass through a partition or randomly pass through inside the column. Such lowering of the cleaning ability appears noticeable in case of using the method disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-144716, as the cleaning method using the active species. Further, when the power of generating plasma is increased to avoid lowering of the cleaning ability, as disclosed in Jpn. Pat. Appln. KOKOKU Publication No. 1-22978, oxidization or fluorination of the surface near the generating portion is intensified.
Further, in the method of removing an oxidized film and a fluoride film by heating the above-mentioned cleaning portion, an apparatus for performing heating is required in addition to an electron beam exposure apparatus, so that there is a problem that the size of the entire apparatus is enlarged and costs are increased. In addition, heating of cleaning portions such as a column and the likes are factors causing degradation in mechanical accuracy.
Furthermore, although active species are generated by using plasma, not only active species but also charged particles such as ions in plasma are introduced into the apparatus in the Jpn. Pat. Appln. KOKAI Publication No. 5-144716 so that charging particles collide with the column, thereby rapidly increasing the temperature of the cleaning portion, since any particular means is not provided for selectively introducing active species. This increase in temperature due to ion collision is a serious problem in case of the method disclosed in Jpn. Pat. Appln. KOKAI Publication 3-3225. Very fine control of time, powers, and the likes are required when cleaning is performed. In addition, the above apparatus (which uses a gas such as plasma to remove contaminants) does not comprises measurement means for measuring the percentage with which removal of contaminants is achieved, and whether or not appropriate processing has been performed cannot be confirmed until the apparatus is actually commenced. In addition, there is a problem that if removal of contaminants is insufficient, cleaning is performed again so that time for vacuum exhaustion is wasted and operation rate decreases.
Further, although it has been proposed a method of irradiating a charged beam and estimating the extent of procedure of cleaning on the basis of a change in the current thereby to measure cleaning effects (Jpn. Pat. Appln. KOKAI 63-313458), it is considered difficult to apply this method to a cleaning method using a gas such as plasma. This is because a high vacuum (of approximately 10.sup.-5 Torr) is required to irradiate a charged beam while cleaning with use of a gas such as plasma is carried out under low atmospheric pressure (of approximately 0.1 Torr).
Meanwhile, since means for generating a cleaning gas and means for exhausting a cleaning gas are formed to be integral with a column in a conventional charged beam apparatus (Jpn. Pat. Appln. KOKAI Publication No. 1-22978), there is a problem that the charged beam apparatus itself is influenced by the generating and exhausting means. For example, there is a problem that an oscillation is generated in the apparatus itself by the above generating means and the exhausting means, thereby lowering drawing precision, and exhaustion in the column cannot be smoothly performed.
Further, the following problem occurs in case of using a plurality of charged beam apparatuses each having a cleaning function are used. That is, costs for the entire apparatus increase since the generating means and the exhausting means are required for each charged beam apparatus.
As has been explained above, cleaning is performed by removing contaminants with use of plasma or active species, in a conventional electron beam exposure apparatus.
However, when the internal space of the column is divided into a plurality of independent areas, and when a gas is made flow randomly in the column, there is a problem that cleaning abilities of plasma and active species, and in particular, the cleaning ability of the active species is greatly decreased (a first problem).
In addition, there is a problem that the plasma forms an oxide film or a fluoride film which causes drifting. Therefore, a method has been proposed in which cleaning portions are heated after cleaning is performed with use of active species having a smaller oxidation force than plasma (ions), cleaning portions are heated thereby to remove an oxide film and a fluoride film.
However, in this method, since an apparatus for performing heating is required, there is a problem that the size of the entire apparatus and costs thereof are increased. In addition, cleaning portions of the column and the likes are heated to a high temperature, and mechanical accuracy is lowered. Even when the column is allowed to be heated, the oxide film formed or Ni, Fe, Cu etc cannot be removed by heating. (a second problem).
Further, another problem is that, although active species are generated with use of plasma, since a conventional apparatus does not particularly comprise means for selectively introducing active species, not only active species but also ions in plasma are introduced into the apparatus so that charged particles collide with cleaning portions of the column, thereby rapidly increasing the temperature of the cleaning portions, and that the mechanical accuracy is lowered and the advantage obtained by using active species for a cleaning is lost (a third problem).
In addition, since means for measuring the degree of accomplishment of removing internal contaminants is not comprised, whether or not appropriate processing has been carried out is not confirmed before actual drawing is performed. Furthermore, if removal of contaminants is insufficient, cleaning is performed again so that time required for vacuum exhausting is wasted, and the operation rate is lowered (a fourth problem).
Further, since the means for generating a cleaning gas and the means for exhausting a cleaning gas are formed to be integral with the column, the charged beam apparatus itself is badly influenced by the exhausting means during normal operation. In addition, when these kinds of apparatuses are used, costs are increased (a fifth problem).